A hydronic network typically employs water, or water-glycol mixtures, as the heat-transfer medium in heating and cooling systems. Some of the oldest and most common examples of hydronic networks are steam and hot-water radiators. In large-scale commercial buildings, such as high-rise and campus facilities, a hydronic network may include both a chilled water loop and a heated water loop to provide both heating and air conditioning. Chillers and cooling towers are often used separately or together to cool water, while boilers are often used to heat water. In addition, many larger cities have a district heating system that provides, through underground piping, publicly available steam and chilled water.
There are various types of hydronic networks, such as steam, hot water, and chilled water. Hydronic networks are also often classified according to various aspects of their operation. These aspects can include flow generation (forced flow or gravity flow); temperature (low, medium, and high); pressurization (low, medium, and high); piping arrangement; and pumping arrangement. Hydronic networks may further be divided into general piping arrangement categories, such as single or one-pipe; two pipe steam (direct return or reverse return); three pipe; four pipe; and series loop.
Some hydronic networks are balanced when installed. However, hydronic networks can be difficult to balance due to several factors. Example factors can include unequal lengths in supply and return lines and/or a larger distance from a boiler (larger distances may result in more pronounced pressure differences). Operators often have several options in dealing with these types of pressure differences. For example, the operators could minimize distribution piping pressure drops, use a pump with a flat head characteristic (include balancing and flow measuring devices at each terminal or branch circuit), and use control valves with a high head loss at the terminals. Hydronic networks can be balanced in some cases by a proportional method, while in other cases the hydronic networks are simply not balanced.
When balancing a hydronic network, an installer or operator often needs to calculate a desired flow rate and differential pressure for the hydronic network. After that, the installer or operator often needs to adjust each valve in the network multiple times until the pressure differential and flow rate in the network are at the desired levels.